Nickel-chromium-iron alloy

ABSTRACT

A strongly age-hardenable alloy having low annealed base hardness, high strength in the aged condition, excellent weldability and unexpectedly good machinability contains about 35 percent to about 46 percent nickel, about 12 percent to about 20 percent chromium, about 1.25 percent to about 2.5 percent titanium, about 2.25 percent to about 3.5 percent columbium, up to about 0.08 percent carbon, about 0.0005 percent to about 0.006 percent boron, about 0.05 percent to about 1 percent aluminum and the balance essentially iron.

United States Patent Eiselstein et al.

[ 1 May 16,1972

1541 NICKEL-CHROMIUM-IRON ALLOY [72] Inventors: Herbert LouisEiselstein; Edward Frederick Clatworthy, both of Huntington, W. Va.

The lnternational Nickel Company, Inc., New York, N.Y.

[22] Filed: Mayll,1970

[21] Appl.No.: 36,420

[73] Assignee:

Related U.S. Application Data [63] Continuation-in-part of Ser. No10,004, Feb. 9, 1970, which is a continuation-in-part of Ser. No.766,611,

Oct. 10, 1968.

[52] U.S. Cl ..75/l24, 75/128 R, 75/128 G, 75/128 T [51] Int. Cl ..C22c39/20 [58] Field of Search ..75/124, 1286 [56] References Cited UNITEDSTATES PATENTS 3,212,884 10/1965 Soler ..75/124 2,801,916 8/1957Harris... ....75/128 G 3,540,881 11/1970 White ..75/128 G PrimaryExaminer-l-lyland Bizot Attorney-Maurice L. Pinel 57 ABSTRACT 7 Claims,No Drawings NICKEL-CHROMlUM-IRON ALLOY The present application is acontinuation-in-part of our co pending US. application Ser. No. 10,004filed Feb. 9, 1970, which in turn is a continuation-in-part of US.application Ser. No. 766,611, filed Oct. 10,1968.

The art pertaining to age-hardenable nickel-chromium andnickel-chromium-iron alloys having high strength and ductility atatmospheric temperatures and at temperatures up to say l,300 F. is nowat a well-developed state. However, despite intensive development workover perhaps the past 30 years, problems still remain in this area.These problems include the provision of big ingots of satisfactoryquality for conversion into sheet and other forms by rolling, hot andcold workability, transverse ductility, machinability, weldability, etc.Alloys of the type under consideration generally contain substantialquantities of elements such as titanium, aluminum, columbium, etc., toconfer hardenability thereto. Many other elements including molybdenum,tungsten, etc., may also be included for the purpose of raising elevatedtemperature properties of the alloys. One result of the high alloycontent employed is that the alloys at the ingot stage are stiff even atthe high soaking temperatures employed prior to hot working so that itbecomes an extremely difficult problem to reduce the ingots by hotworking in conventional equipment. Another problem encountered inproducing large ingots is that of difficulty in melting, a conditionwith is attributable to segregation in cooling and is evident asfreckles in the macrostructure of the ingot. In a number of alloyscurrently being used, this problem cannot be solved by homogenizing heattreatments and hot working and can be sufficiently severe to causerejection of ingots. The problem is particularly acute in relation tobig slab ingots of sufficient width for conversion into plate and sheet.

Alloys of the type under consideration are frequently required to beprovided in the form of sizable forgings which are then machined intoproduct forms such as turbine wheels, shafts, rings, etc. Goodmachinability thus is highly important since, in many cases, substantialquantities of metal are removed by machining. Difficulties frequentlyhave been encountered by way of high tool wear, poor surface finish,etc., in machining many of the stronger alloys currently being used.These difficulties have led to high costs and unsatisfactory results inmachining.

Another problem frequently encountered with the stronger alloyscurrently used is that of weldability, particularly as ap plied to sheetform. Thus, weld cracking has been encountered both in connection withthe welding operation itself and also when the weldment was age hardenedto restore high strength after welding. In some alloys, the problem isso severe that the alloys are not considered commercially weldable.

Still another problem is that of providing ductility in the directiontransverse to the working direction in such alloys. This problem isparticularly severe in rotating parts such as shafts, rotors, rings,etc., which are highly stressed in service at temperatures over therange from about room temperature to about l,400 F. Many present alloyswhich are strong at room temperature and at elevated temperaturesdevelop low ductility, e.g., a room temperature tensile elongation of 2percent or less, whenmeasured in a direction transverse to the workingdirection. Such parts are usually hot worked to rough shape by processessuch as forging, pressing, rolling, etc., and are then machined tofinish dimensions, and the low transverse ductility which characterizesprior alloys has been a source of concern to designers.

It is to the solution of the foregoing and other problems that theinvention is principally directed.

It is an object of the present invention to provide a stronglyage-hardenable nickel-chromium-iron alloy which can be produced in largeingot forms by conventional melting and ingot casting.

It is another object of the present invention to provide an improvedage-hardenable nickel-chromium-iron alloy having improved machinabilityand weldability both in the annealed and in the age-hardened condition.

it is a further object of the invention to provide a stronglyage-hardenable nickel-chromium-iron alloy which is relatively soft inthe annealed condition and is readily hot workable.

Still another object of the invention is to provide an alloy whichdevelops good transverse ductility in the hot worked and age-hardenedcondition.

Other objects and advantages of the invention will become apparent fromthe following description.

Generally speaking, the present invention is directed to anage-hardening alloy having good melting characteristics, a low basehardness in the annealed condition together with good machinability,good transverse ductility, and weldability comprising about 35 percentto about 45 percent or 46 percent nickel, about 12 percent to about 18percent or 20 percent chromium, about 1.25 percent to about 2.5 percenttitanium, about 2.25 percent to about 3.5 percent columbium, with thesum of the percentages of columbium and titanium being at least equal toabout 4 percent, at least about 0.05 percent or 0.07 percent to about 1percent aluminum, not more than about 0.08 percent carbon, 0.0005percent to about 0.006 percent boron and the balance essentially iron.Preferably, the alloy contains about 14.5 percent to about 17.5 percentchromium, about 39 percent to about 44 percent nickel, about 1.5 percentto about 2 percent titanium, about 2.5 percent to about 3 percentcolumbium, at least about 0.001 percent boron, and about 0.1 percent toabout 0.4 percent or 0.5 percent aluminum.

In the alloy, the nickel and iron contents are highly important and thenickel content is controlled within the range of about 35 percent toabout 45 percent with the balance of the alloy being iron so as tosecure a strong age-hardening effect despite the fact the alloy containsrelatively small amounts of age-hardening ingredients. Chromium impartsoxidation resistance. Chromium at a level of about 15 percent or about15.5 percent maintains the alloy in an essentially non-magneticcondition, i.e., maintains permeability below about 1.02. The principalage-hardening ingredients in the alloy are titanium and columbium whichare employed in amounts of about 1.25 percent to about 2.5 percent andabout 2.25 percent to about 3.5 percent, respectively, with the totalcontent of these elements being at least about 4 percent to obtain goodstrength in the age-hardened alloy. Aluminum is employed in amounts notexceeding about 1 percent since paradoxically it is found that aluminumtends to reduce yield strength of the age-hardened alloy in someage-hardened conditions. Preferably, the aluminum does not exceed about0.4 percent in order to mitigate the effect of this element in reducingstrength of the age-hardened alloy and further to avoid the possibilityof strain age cracking in welds. However, aluminum plays an importantrole in the alloy and must be present in a small significant amount ofat least about 0.05 percent or about 0.07 percent or 0.1 percent inorder to confer transverse ductility to the alloy in the hot worked andaged condition. In this respect, aluminum appears to cooperate with thecontrolled boron content employed in the alloy. Titanium is preferablyemployed in amounts of at least about 1.5 percent to about 2 percent andcolumbium in amounts of about 2.5 percent to about 3 percent. Suchamounts of the primary agehardening ingredients confer strongage-hardenability to the alloy, minimize the possibility of undesirablesegregation in the production of large ingots and provide a low basehardness in the annealed alloy. Tantalum may be substituted forcolumbium in equi-atomic amounts, but is less preferred because of thehigh atomic weight of tantalum. The carbon content of the alloy does notexceed about 0.08 percent, preferably not more than 0.06 percent. As aresult, only a small amount of carbide is found in the microstructure ofthe alloy. Boron in the alloy contributes to stress-rupture ductility,but can lead to undcrbead cracking in welds and acts toward reduction oftransverse ductility. Accordingly, the boron content does not exceedabout 0.006 percent and is present in amounts of about 0.0005 percent toabout 0.005 percent.

Alloys provided in accordance with the invention contain not more than0.35 percent manganese, not more than about 0.35 percent silicon, notmore than 0.3 percent copper, and not more than about 1 molybdenum.Molybdenum in amounts exceeding about 1 percent significantly stiffensthe alloy matrix both at room temperature and at metal hot workingtemperatures and increases processing difficulties particularly in largesections. Impurities such as sulfur and phosphorus are kept to lowlevels not exceeding about 0.015 percent each. Cobalt does notcontribute to useful properties in the alloy and is not deliberatelyadded thereto. This element, like molybdenum, raises cost and cobalt isobjectionable for uses in which radiation may be encountered.

The alloy is readily workable both hot and cold and can be aged eitherdirectly in hot or cold worked product forms or after an anneal in thetemperature range of about 1,700 F. to about 1,950 F. or about 2,000 F.Annealing times of about 1 hour per inch of section are satisfactory.The alloy responds to aging treatments over the temperature ranges ofabout 1,l F. or 1,200 F. to about 1,400 F. which may be carried out forperiods of time of about 4 hours to about 16 hours, e.g., about 8 hours.It is found that material annealed at temperatures above 1,750 F.develops better 1,200 F. stress-rupture ductility if an intermediateaging step in the temperature range of about l,500 F. to about 1,600 F.,e.g., 1,550 F., for a time period of about 1 to about 8 hours, e.g., 3hours, is also employed, thereby providing a three-stage agingtreatment. A preferred aging treatment comprises a heating in thetemperature range of about 1,300" F. to about 1,400 F. for about 8 hoursfollowed by furnace cooling at a rate of about 100 F. per hour to 1,200F. and holding at about 1,150 F. to 1,200 F. for about 8 hours. In theannealed condition, the alloys are quite soft and ductile, generallyhaving room temperature yield strengths as determined in wroughtmaterial in the range of about 35,000 to about 50,000 pounds per squareinch (p.s.i.). In the aged condition, wrought products made of the alloywill have in sections ranging up to about 3 inches a room temperatureyield strength of about 140,000 p.s.i. or 150,000 p.s.i. or highertogether with substantial ductility.

The low annealed base hardness and high strength in the aged conditionprovide substantial advantages in the alloy from the standpoints of millproduction, component fabrication and end use. In addition, the alloydemonstrates excellent weldability in both annealed and aged conditions,and weldments can be aged without encountering weld cracking.Furthermore, the alloy provides unexpectedly good machinability in boththe annealed and aged conditions. When compared on an equal strengthbasis with prior age-hardenable nickel-chromium alloys intended forelevated temperature service, the machinability of the alloy is verygood indeed.

In order to give those skilled in the art a better understanding and/orappreciation of the advantages of the invention, the followingillustrative examples are given:

EXAMPLEI A series of 15 kilogram vacuum melted heats was prepared andcast into 4 inch X 4 inch ingots. The ingots were homogenized at about2,100 F. to 2,150 F. for 12 to 16 hours and air cooled. The material wasreheated and forged to 2-% inch square bars. Transverse slices preparedfrom the forgings demonstrated that the material was sound and devoid ofsegregation. The analyses of nine heats prepared as aforedescribed areset forth in the following Table I:

TABLEI Percent Alloy No. 0 Ni 01' A1 Cb Ti 13 Fe 14.91 0.22 3.06 1.24N.d. Bal. 14.64 0.21 2.91 1.45 0.001 Bel. 15.00 0.18 2.77 1.42 0.0012Bal. 14.82 0.10 2.78 1.42 0.0013 Ba]. 15.12 0.20 2.41 1.86 0.0012 Bal.15.27 0.19 2.54 1.90 0.001 Bal. 14.07 0.10 2.52 1.83 0.001 Bal. 15.880.22 2.71 1.68 0.0006 Bal. 15.82 0.19 2.71 1.63 0.0043 Ba].

NOTE.Ihe alloys in Table I contained about 0.01% manganese,

about 0.04% to 0.07% silicon, not more than 0.03% copper, and not morethan 0.006% sulfur.

1V .d iotdgtermined.

material from the 244 inch square forgings was subjected to roomtemperature tensile testing in various conditions of heat treatment withthe results set forth in the following Table II:

TABLE 11 Yield strength (0.2% Tensile I offset), strength, EL, R.A.,Alloy No Condition K s.1 K s.i. percent percent 1 As forged, aged 156.0174.0 13. 0 21. 0 Annealed 1,000 F 34. (i 03. 3 51. 0 57. 0 Annealed1,000 F., aged 154.0 178.0 16.0 27.0 Annealed 1,050 F 46. 5 100. 0 44. 048. 0 Annealed 1,050 F., aged 153. 5 176.0 16. 0 24. 5 Annealed 1,050F., aged 3 151.5 178.0 15.0 25. 8 2 As forged, aged 2 161.0 170. 5 16. 020. 5 Annealed 1,000 F 34. 8 01. 7 48. 0 54. 7 Annealed 1,000 F., aged151. 5 178.0 19. 0 26. 2 Annealed 1,950 F 36. 4 92. 7 45. 0 45. 8Annealed 1,950 F., aged I55. 0 175. 5 l. 0 17. 5 Annealed 1,950 F., aged3 152. 5 177. 5 19. 0 80. 0

3 As forged, aged 156. 0 178. 5 15. 0 26. 8 Annealed l,800 F-.. 39. l)96. 8 39. 0 39. 0 Annealed 1,800 F., ag 153. 0 181.0 21. 0 30. 1Annealed 1,000 F 35. 6 04. 0 50. 0 60. 3 Annealed 1,900 F., aged 152.0170. 5 21.0 37. 8 Annealed 1,950 F 35. 6 03. 3 54. 0 58. 3 Annealed1,950 F., aged 2 154. 5 178. 0 10. 0 33. 5

4 As forged, aged 2 157.0 178.5 17.0 31. 1 Annealed 1,900 F 35. 3 93. 440. 0 50. 3 Annealed 1,900 F., aged 152. 5 170. 5 22.0 38. 0 Annealed1,950" F 37. 1 95. 3 53. 0 53. 3 Annealed 1,950 F., aged 2 153. 5 178. 020.0 34. 0 Annealed 1,950 F., aged 3 154. 5 178. 5 17. 0 25. 0

5 Annealed 1,950 F 35. 8 95. 8 52. 0 57. U Annealed 1,050 F., aged 151.5 180. 5 20. 0 34. 0 Annealed 1,950 F., aged 156.0 182. 5 18. 0 33.5Annealed 1,050 F., aged 4 152.5 182. 0 18. 0 30. 7

6 Annealed 1,1100" F 36. 6 07. 3 50. 0 57. Annealed 1,I00 F., aged 3155. 5 183. 5 10. 0 .28. 0 Annealed 1,050 F 47. 6 04. 7 40. 0 57. 3Annealed 1,050 F., aged 155. 0 180. 5 16.0 2-1. 0 Annealed 1,050 F.,1111011 157. 5 183. 5 l6. 0 33 0 Table ll- Continued 1 Aged 1,825 F./8hours, furnace cool 100 F./hr. to 1,200 F., hold 8 hours, air cool. 2Aged 1,350 F./8 hours, furnace cool 100 F./hrs. to 1,200 F., hold 8hours, air cool. 3 Aged 1,375 F./8 hours, furnace cool 100 F./l1r. to1,200 F., hold 8 hours, air cool.

4 Aged 1,400 F./8 hours, furnace cool 100 F./hr. to 1,200 F., hold 8hours, air cool.

K s.i.=thousands of pounds per square inch. El.=elongation. R.A.=reduction in area.

NorE.Annealing times one hour, followed by air cool.

Forged material from Alloys Nos. 8 and 9 were subjected tostress-rupture resting at 1,300 F. and 75,000 p.s.i. with the about 0.08percent manganese, about 0.11 percent silicon, 39.73 percent nickel,15.99 percent chromium, 0.24 percent results set forth in the followingTable III. aluminum, 1.61 percent titanium, 2.83 percent columbium,TABLE n 0.0026 percent boron and the balance essentially iron. The ingotwas press forged to a 15% inch octagon which was then Life to machinedto a 14 inch diameter round. Three inch slices were Alloy Rupture along"RA" cut from the head and toe ends of the forgingand were exconditionhours ammed 1n the transverse and longltudmal directions. Ex-

amination demonstrated that the material was devoid of 8 Annealed "50F"segregatlon, and indicated that large slab ingots could be aged (3)156.9 155 produced from the alloy usmg conventlonal vacuum-melting 8Annealed 1850F., techniques without encountering melting difficulties.Three aged (3) 0 156-8 7 inch square material was forged to 2V8 inchsquare bars with 9 gzii g 166 5 23 5 46 forging temperatures of 1,900 F.and 2,050 F. Tensile, im- 9 Annealed 50F pact and stress-ruptureproperties of the two forgings were aged (3) 154.4 16.5 28.6 determinedwith the results set forth in the following Tables 1V and V: 35

TABLE IV Y.S. (0.2% CVN, ft. ll)s. ofi'set), I.S., El., R.A., Conditions.i. K s.i. percent percent Room 320 F.

Forging temperature: 1,900 F.

Annealed 1,700 F., aged 15s. 0 174.0 11.0 19. 0 Annealed l,750 F., aged152.0 179. 0 16. 0 21. O 27. 5 26 Forging temperature: 2,050" F.

As forged, aged 3 156. 0 182. 5 18.0 29. 0 Annealed 1,700 F., aged 159.0187. 5 16. 0 22. 5 Annealed 1,750 F., aged 156.5 183. 5 17.0 31.8 22. 520 Y.S.=yield strength. T.S.=tensile strength. CVN, ft.-lbs.=CharpyV-notch, foot-pounds.

TABLE V Stress rupture test Life, El., R.A., Co ditio conditions hourspercent percent Forging temperature: 1,900 F.

Annealed 1,700 F., aged 1,200" F./100 K s.i 160. 2 3.0 3.0 Do.3 1,300F./75 K s.i 104. 5 2. 5 4. 5 Annealed 1,750 F., aged 3 1,300 F./75 K s71. 2 4. 0 7. 5

, Forging temperature: 2,050" F.

Annealed 1,700 F., aged 3 1,3o0 F./75 K s.i 101. 3 8. 5 11.5

EXAMPLE I1 Portions of the remainder of the ingot were converted into A24 inch diameter vacuum-arc ingot was prepared from a composition whichcontained about 0.01 percent carbon,

inch diameter hot rolled bar stock and to 0.062 inch diameter coldrolled sheet. The tensile properties, Charpy V-Notch impact andstress-rupture properties of the material in the bar stock and sheetproduct forms are set forth in the following Tables VI, VII, VIII, IXand X:

were then welded in the holes using the manual argon-shieldedtungsten-arc process, with matching filler metal being used in TABLE VIHot rolled -inch diameter bar Y.S. T.S., K 5.1. Test (0.2

temp., offset) Smooth Notched EL, R.A., Condition F. K s.i. bar barpercent percent As rolled Room 78. 3 41 64. 5 As rolled aged 3 Room 164.5 22 43. 2 Annealed 1,750 F Room 68. 45 50. 7 Annealed 1,750 I11, agedRoom 158. 0 100. 0 256. 0 21 42 0 3 -320 180. 0 235. 0 281. 0 22 37. Do3 1, 200 133. 0 147. 0 218. 0 23 48 Ii-r of notched b:tl'=li.3.

TABLE VII the case of the 1,950 F. annealed specimen. The welds were Hotrolled inch diameter bar aged at l,375 F. for 8 hours, furnace cooled at100 F. per hour to 1,200 E, held for 8 hours at 1,200 F., air cooled.XQBA L 333, f-g gfg Simulated repair welds were then made over about 90of arc C nditi Room 108 cycles at opposite sides of the disc within theinitial weld using the AS rolled 135 5 239. 5 70 same welding techniqueand the welds were again aged using As rolled, aged 26.5-27.5 30-305 80the same aging cycle. No weld cracks were detected at any I H280 'ijjjij1%,, ig 98 stage of the operation, indicating good weldability for thealloy in this severely restrained test.

Machinability tests were conducted on a 3 /4 inch diameter TABLE VIIIforging as annealed at l,850 F. for 1 hour, air cooled, and in Hotrolled %-ineh diameter bar the annealed and aged condition (aged l,375F. for 8 hours, Life hours furnace cooled 100 F. per hour to 1,200 F.,held 8 hours at 1,200" F., air cooled). In the machinability tests, aninstrugfi gx gggi gg}. fi g g, mented variable speed lathe was employedusing single point D h carbide tools. Each test tool was ground with a 0back rake i'ggo igg' ,5 2 angle, a 5 side rake angle, a 5 end clearanceangle, a 5 side 1I300 F./75 K s.i.: 39. 6 218.1 in 37. 5 clearanceangle, 15 end cutting edge angle, a 15 side cutting NOTE.The materialwas annealed at 1,750 F. for one hour, aged 3. edge angle and a U3? Inchnose radlus' Tool pomt D=disc0ntinued; KT of notched bar=6.3. was takenas 0.015 inch flank wear. The cutting site was TABLE IX Cold rolled0.062 inch sheet Y.S. 'I S., K s 1 Test 0.2% temp, oll'set), SmoothNotch EL, Condition F. K s.i. specimen specimen" percent As rolled Room110.0 137. 5 u As rolled, aged 3 Room 187. 5 210. 5 Annealed 1,750 FRoom 45. 0 111. 5 Annealed 1,750 F., aged 3 Room 176. 5 200.5 D0 3 1,200 144. 5 168. 5 Annealed 1,850 F Room 44. 3 115. 5 Annealed 1,850 F.,aged 3 Room 175.5 100. 5 D0 3 320 206. 0 260. 0 D0 3 1, 200 140 162. 5Annealed 1,950 F Room 42. 0 111.0 Annealed 1,950 F., aged 3 Room 170.0193.5 D0 3 320 195. 0 254. 5 1, 200 137. 5 160. 0

K of notched specimen=20.

TABLE X Cold rolled 0.062 inch sheet Stress-rupture test Life, El.,Condition conditions hours percent Annealed 1,750 F., aged 3 1,200F./100 K s.l 196.6 7 Annealed 1,850 F., aged 1,200 F./100 K s.i 113. 0 4Annealed 1,950 F., aged 3 1 200 F./100 K s i 123. 5 2 Annealed 1,760 F.,aged 3 1 300 F./75 K s 1 03.1 14 Annealed 1,850 F., aged 3 1,300 F./75 Ks. 123.5 6 Annealed 1,950 F., aged 3 1,300 F./75 K 5.1 85. 8 5

Test specimens from the sheet material were subjected to the severerestrained welding test identified as the Pierce Miller patch weld test.In this test, a specimen of 0.062 inch cold rolled sheet of the alloy 4inches square and with a central 2 inch diameter hole was weldedsymmetrically to a face of an age-hardenable nickel-chromium alloystrong-back made of Va inch thick plate 6% inches square and with a 3inch diameter central hole so as to leave the hole in the sheet specimenunsupported. Two such assemblies were made which were annealed at l,750F. for 1 hour and l,950 F. for 1 hour, respecflooded with coolant. Acobalt-bonded general purpose carbide tool of the WTiC type having ahardness of 91 on the Rockwell A" scale was employed. Data were obtainedwith 0.050 inch depth of cut at two feed rates and with two wearlandconditions on the carbide tool point. Using a feed rate of 0.00825 inchper revolution with an 0.015 inch wearland, the cutting velocity for a30 minute tool life (V30) was determined as being l68 surface feet perminute for annealed material and 182 surface feet per minute forannealed and aged material. With the heavier 0.01175 inch per revolutiontively. Two inch diameter discs of matching sheet material feed rate andwith an 0.030 inch wearland on the tool point,

the cutting velocity for a 30 minute tool life was determined to be 164surface feet per minute for annealed material and 168 surface feet perminute for annealed and aged material. The machinability index for thematerial was determined on a comparative basis with othernickel-chromium alloys converted to a machinability index factor usingthe formula Machinability index (Mi) Material tested (V30) X100 10Standard material (V30) Using as the standard material the forged alloyof the present invention in the'annealed condition, M, values weredetermined in comparison with five other nickel-chromium alloys (ofwhich Alloys A, B and E are age-hardenable, while Alloys C and D arenot) with the results set forth in the following Table X1:

TABLE XI Material Condition M, Alloy of this invention Annealed 100Alloy of this invention Annealed and aged I08 Alloy A Hot rolled or hotrolled 50 and aged B Annealed 39 C Annealed 229 D Hot rolled 250 DAnnealed 230 E Hot rolled 47 E Hot rolled and equalized 72 E Hot rolledand equalized 66 and aged Alloy A 52.5% Ni, 19% Cr, 0.5% Al, 0.9% Ti, 5%Cb, 3% Mo, balance Fe. Alloy B= 73% Ni, 15.5% Cr, 0.7% A1, 2.5% Ti,0.95% Cb, balance Fe. Alloy C= 76% Ni, 15.5% Cr, balance Fe.

Alloy D= 32.5% Ni, 21% Cr, 0.38% Al, 0.38% Ti, balance Fe.

Alloy E= 42.7% Ni, 13.5% Cr, 2.5% Ti, 0.25% Al, 6.2% Mo, balance Fe.

percent carbon, 42.46 percent nickel, 14.33 percent chromi um, 2.09percent titanium, 2.95 percent columbium, 0.06 percent aluminum, 0.009percent boron, balance iron. Alloy H with a high boron content of 0.009percent outside the invention was thus found to have poor machinability.However, from machinability tests using the 0.025 inch depth of cut toconserve material, it was found that good machinability was obtainedwhich was relatively unaffected by variations in aluminum content andboron content over the ranges set forth hereinbefore for alloys withinthe invention. The improved machinability which characterizes alloyswithin the invention has not been explained from a theoretical point ofview. It was determined that about one horsepower per cubic inch perminute was required in cutting the alloy of the invention and thisfurther demonstrated the excellent, quite unexpected, level ofmachinability provided in the alloy.

EXAMPLE III In order to demonstrate the effects of aluminum and boron onroom temperature transverse ductility, four lS-kilogram vacuum meltswere prepared, of which Alloys l0 and 11 were within the invention andAlloys F and G were outside the invention, with compositions as shown inthe following Table XII:

TABLE XII Cl) Ti 13 1 I 2. .18 2. l0 0. 0014 3. 05 2. 27 0. 0013 2. JD2. 18 0. 0002 2. 08 2. 21 0. 0034 Bal. Bal.

The ingots of the foregoing alloys were homogenized at 2,100 F. for 16hours and were forged to 2A-inch square bar. Longitudinal and transversetensile properties were determined at room temperature and at l,200 F.in the as forged, annealed l,800 F. for 1% hour at temperature), andannealed plus aged conditions. The aging treatment comprised a heatingat 1,550F. for 3 hours, air cool, a heating at 1,325F. for 8 hours, afurnace cool at F. per hour to l,l50F., a hold at 1,150F. for 8 hoursand an air cool. Stress-rupture properties in the longitudinal directionwere determined at 1,200F. and 100,000 psi using combination smooth andnotch specimens. The results of the tensile tests are set forth in thefollowing Table XIII:

TABLE XIII Tensile test results Room temperature 1,200" F.

Yield Yield strength strength (0.2% Tensile (0.2% Tensile offset),strength Percent Percent ofiset), strength Percent Percent Alloy NoCondltion K s.i. K s.i. elong. R.A. K s.i. K s.i. elong. R.A.

10 A5 for ed 81. 5 32 32 Annea le 43.0 106.5 44 49. 5 Annealed plus aged(L) 141 139 17 21 123 22 48 Annealed plus aged (T) 50 85 8 5 122 142 1825 11 As for ed 113 167 18 23 Annezfied 50 115. 5 43 44. 5 v Annealedplus aged (L) 158 194 18 25 130 2 43 Annealed plus aged (T) 154. 5 187.5 8 12 126. 5 145. 5 4 30 5 Astor ed 73 7 28 33 Annea led 41. 5 106 4040. s Annealed plus aged (L) 144 188 18 27 122. 5 146 24 51 Annealedplus aged ('I) 151 163 2 8 120 5 5 5 g 7 4 A for ed 109 140 16 22 i i iv V g l p (J Anneaigd A 44: 104 34 36. 5 v r r i A A 7 7 7 7 7 VAnnealed plus aged (L) 193 18 26 120 14G 24 51 Annealed plus aged (T)157. 5 173 4 10 124 144 5 21 g 5 EXAMPLE lV An alloy containing about0.01 percent carbon, about 0.1 percent manganese, about 0.06 percentsilicon, about 40.6 percent nickel, about 16.14 percent chromium, about0.27 percent aluminum, about 1.76 percent titanium, about 2.68 percentcolumbium, 0.0025 percent boron, and the balance essentially iron, inaccordance with the invention was melted in a vacuum induction furnace.Metal from the melt was cast in air into a vertical slab ingot weighingabout 5,500 pounds and measuring 1 1 inches by 45 inches by 50 inchesusing a flux casting procedure. The ingot was heated to 2,050 F. andforged to inches thick, was then soaked for 16 hours at 2,050 F. androlled to 6 inches thick, reheated to 2,050 F. and rolled to 3 inchesthick. The 3 inch thick slab was reheated to 2,050 F. and rolled to ahot band about /4 inch thick. Excellent malleability was evidentthroughout the procedure. A transverse slice cut just below the headcrop of the 3 inch slab was freckle free. The hot band was mill annealedin the temperature range 1,900 F. to 2,000 F. and a portion therefromwas further annealed for 1 hour at 1,750 F. In this condition, thematerial displayed a yield strength (0.2 percent offset) of 42.7 k.s.i.,a tensile strength of 100.5 k.s.i. and an elongation of 49 percent. Aportion of the annealed material was then aged by heating at 1,350 F.for 8 hours, furnace cooled to 1,150 F. and held for 8 hours. In theaged condition, the material displayed a yield strength (0.2 percentoffset) of 152 k.s.i., a tensile strength of 188 k.s.i. and anelongation of 22 percent. This example illustrates the amenability ofthe alloy to production of flat rolled products using conventionalmelting and slab ingot procedures, with the attainment of high strength.

EXAMPLE V In order further to illustrate the effect of aluminum contentin alloys provided by the invention, a series of kilogram vacuuminduction heats was produced to essentially the same base composition;namely, about 0.04 percent carbon, about 0.22 percent manganese, about0.16 percent silicon, about 40.3 percent nickel, about 16.7 percentchromium, about 2 percent titanium, about 3.1 percent columbium, about0.0028 percent boron, and the balance essentially iron and containingaluminum in varying amounts, i.e., 0.033 percent (Heat 12A), 0.12percent (Heat 128), 0.2 percent (Heat 12C), 0.44 percent (Heat 12D),0.65 percent (Heat 12E) and 0.9 percent (Heat 12F). The ingots wereforged to 9/16 inch square bar. The bars were annealed at 1,900 F. forone-half hour, air cooled, and then aged at 1,550 F. for 3 hours, at1325 F. for 8 hours, furnace cooled at the rate of 100 F. per hour to 1,1 50 F. held at 1,150 F. for 8 hours and then air cooled. The annealedand aged bars were subjected to room temperature and 1,200 F. tensiletests with the results as shown in the following Table XlV:

TABLE XIV Room Temperature Tensile Tests Yield Strength 12 1200F.Tensile Tests 12A 126.5 143.5 25 52.5 12B 128 147 23 49.5 12C 134 148.522 43 12D 129 148 21 47 12E 124 146 24 44.5 12F 131.5 153.5 25 54 Inaddition, annealed and aged bars of the alloy were subjected tostress-rupture testing at 1,200 F. and 100,000 psi stress with theresults set forth in the following Table XV:

The data provide further confirmation that best yield strength andrupture life are exhibited in the alloy in the condition of heattreatment employed in this Example V when the aluminum content isbetween about 0.2 percent and about 0.45 percent.

Products produced from the alloy provided in accordance with theinvention include sheet, plate, strip, bar, tubing, extruded shapes,forgings, etc., useful in turbine wheels, shafts, rings, pressurevessels, high temperature piping, bolts, springs, etc.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. An age-hardenable alloy having good melting characteristics, a lowbase hardness in the annealed condition and good machinabilityconsisting essentially of about 35 percent to about 46 percent nickel,about 12 percent to about 20 percent chromium, about 1.25 percent toabout 2.5 percent titanium, about 2.25 percent to about 3.5 percentcolumbium, with the sum of the percentages of titanium and columbiumbeing at least about 4 percent, at least about 0.05 percent to about 1percent aluminum, about 0.0005 percent to about 0.006 percent boron, upto about 0.08 percent carbon, up to about 0.35 percent manganese, up toabout 0.35 percent silicon, not more than about 0.3 percent copper, notmore than about 1 percent molybdenum, and the balance essentially iron.

2. An alloy according to claim 1 wherein the nickel content does notexceed about 45 percent and the chromium content does not exceed about18 percent.

3. An alloy according to claim 1 containing about 14.5 percent to about17.5 percent chromium, about 39 percent to about 44 percent nickel,about 1.5 percent to about 2 percent titanium, about 2.5 percent toabout 3 percent columbium, and not more than about 0.5 percent aluminum.

4. An alloy according to claim 3 wherein the carbon content does notexceed about 0.06 percent.

5. An alloy according to claim 3 wherein the aluminum content is about0.1 percent to about 0.4 percent.

6. An alloy according to claim 1 wherein the boron content is about0.001 percent to about 0.005 percent.

'7. An alloy in accordance with claim 3 wherein the aluminum is about0.2 percent to about 0.45 percent.

2. An alloy according to claim 1 wherein the nickel content does notexceed about 45 percent and the chromium content does not exceed about18 percent.
 3. An alloy according to claim 1 containing about 14.5percent to about 17.5 percent chromium, about 39 percent to about 44percent nickel, about 1.5 percent to about 2 percent titanium, about 2.5percent to about 3 percent columbium, and not more than about 0.5percent aluminum.
 4. An alloy according to claim 3 wherein the carboncontent does not exceed about 0.06 percent.
 5. An alloy according toclaim 3 wherein the aluminum content is about 0.1 percent to about 0.4percent.
 6. An alloy according to claim 1 wherein the boron content isabout 0.001 percent to about 0.005 percent.
 7. An alloy in accordancewith claim 3 wherein the aluminum is about 0.2 percent to about 0.45percent.